The use of lead salt materials, such as lead sulfide (PbS), lead selenide (PbSe), and lead telluride (PbTe), in photoconductive and photovoltaic applications is well known in the art. Lead salt materials have band gap energies which allow the absorption of radiation in the infrared spectrum. In photoconductive applications, the absorption of infrared radiation by the lead salt material provides a change in its conductivity. The change in the conductivity can be sensed by sensing a current flowing therethrough. In this way, the lead salt material can be used to sense incident radiation. In photovoltaic applications, the absorption of infrared radiation in the lead salt material provides a potential difference. The potential difference can be used to provide electrical power. Accordingly, lead salt materials can be used in optoelectronic devices such as infrared photodetectors, solar cells, and thermoelectric devices, among others.
It is typically desirable to sensitize the lead salt material after is it deposited onto a substrate. The sensitization process produces lead salt material that is sensitive to incident infrared (IR) radiation at higher temperatures, such as room temperature, in comparison to the typical cold temperatures used. Sensitization is usually done by exposing the lead salt material to oxygen. The sensitization can be characterized by measuring the resistivity of the lead salt material.
Iodine is naturally in a solid state that can be liquefied. One method to liquefy is to mix the solid iodine with alcohol and heat the liquefied iodine. An inert gas, such as nitrogen, is passed over the liquefied gas to transport iodine vapor to the intended location. However, use of alcohol may affect subsequent reactions and the method is difficult to control if only a certain amount of iodine gas is desired.
Another method of iodine liquefying involves heating the solid iodine to a temperature below 183° C. where the iodine is subliming at a known rate based on the temperature. An inert gas, such as nitrogen, is introduced and transports the iodine gas to the intended location. However, use of an inert gas may disrupt the partial pressure of the iodine and affect the desired results. Furthermore, the sensitization of lead salt material regions using conventional methods often leads to undesirable differences in resistivity from one lead salt material region to another.
These problems limit the usefulness of any devices formed with lead salt materials fabricated using conventional deposition systems and methods. Hence, there is a need for better systems and methods of a sensitization process for addressing these and other issues.